1. Field of the Invention
The present invention generally relates to an image signal processing apparatus and, more particularly, to an image signal processing apparatus for adaptively correcting color saturation in accordance with information obtained from image data.
2. Description of the Related Art
The dynamic range of an image pickup element is generally about 50 to 60 dB, and the dynamic range of a TV (television) monitor is about 45 dB. To the contrary, the dynamic range of a general object is as wide as 80 to 100 dB. As a means for solving this problem, a technique is described in, for example, U.S. Pat. No. 4,926,247 by the assigner of the present application.
According to U.S. Pat. No. 4,926,247, outputs from a pair of color image pickup elements are added for each of chrominance signals R, G, and B. Only a luminance signal obtained by matrix conversion is logarithmically compressed by a logarithmic compressor. Gain adjustment or the like of the output from this logarithmic compressor is performed, and each chrominance signal is multiplied by a ratio of this output to the original luminance signal, thereby displaying an image with a compressed dynamic range without changing the chromaticity.
In display of an image by using the technique described in Jpn. Pat. Appln. KOKAI Publication No. 63-232591, when the compression ratio of the dynamic range is increased, the color saturation of the image data seems to be emphasized although the chromaticity of the image data is not actually changed, resulting in unnatural display.
This phenomenon typically occurs at a dark portion of the image. Therefore, when the color saturation of the whole image is simply adjusted, and the dark portion is saturation-adjusted to obtain a natural color tone, the color saturation at a bright portion is excessively suppressed.